The El Niño-Southern Oscillation (ENSO) drives variations in terrestrial carbon fluxes by affecting the terrestrial ecosystem via atmospheric teleconnections and thus plays an important role in interannual variability of the global carbon cycle. However, we lack such knowledge on decadal time scales, that is, how the carbon cycle can be affected by decadal variations of ENSO characteristics. Here we examine how, and by how much, decadal ENSO variability affects decadal variability of the global carbon cycle by analyzing a 1,801-year preindustrial control simulation. We identify two different aspects, together explaining~36% of the decadal variations in the global carbon cycle. First, climate variations induced by decadal ENSO-like variability regulate terrestrial carbon flux and hence atmospheric CO 2 on decadal time scales. Second, decadal changes in the asymmetrical response of the terrestrial ecosystem, resulting from decadal modulation of ENSO amplitude and asymmetry, rectify the background mean state, thereby generating decadal variability of land carbon fluxes.Plain Language Summary The El Niño-Southern Oscillation (ENSO) is an important driver of year-to-year variation of the global carbon cycle due to its impacts on the global climate variability. For example, most parts of the tropical land experience drought during El Niño events, and therefore rainforests and savanna regions do not capture well carbon dioxide compared to normal years because a high temperature and a lack of precipitation during El Niño events lead to less photosynthesis over the tropics. This is a well-known feature in year-to-year variation, but not in decadal time scales due to a lack of long-term observations. Here we examine how, and by how much, decadal ENSO variability affects decadal variation in the global carbon cycle by analyzing a 1,801-year Earth System simulation. We found that two different aspects of decadal ENSO variability, associated with decadal changes in the tropical Pacific Ocean and asymmetric characteristics between El Niño and La Niña, drive decadal change in the terrestrial carbon fluxes. As a result, these two aspects together can explain~36% of the decadal variability in the global carbon cycle.It has long been established that the El Niño-Southern Oscillation (ENSO), a predominant mode of climate variability, leads to interannual variability of the global carbon cycle (Key Points: • About 36% of decadal variations in global NBP can be explained by two aspects of decadal ENSO variability • First, decadal ENSO-like variability induces interdecadal changes in terrestrial carbon fluxes via atmospheric teleconnections • Second, decadal ENSO modulations in amplitude and asymmetry lead to decadal NBP variability by changing ENSO-induced residual NBP Supporting Information: • Supporting Information S1

The combined impact of Greenland sea ice, Eurasian snow, and the El Niño–Southern Oscillation (ENSO) on the out‐of‐phase relationship between the Indian summer monsoon (ISM) and Korean summer monsoon (KSM) were investigated through numerical experiments. The results revealed that Indian and Korean summer rainfalls showed nonlinear responses to ENSO and Greenland sea ice forcing when the events co‐occurred. Above‐normal Greenland sea ice and a concurrent La Niña showed a distinct in‐phase relationship with ISM and out‐of‐phase relationship with KSM. Below‐normal and above‐normal Greenland sea ice during boreal autumn surrounded the Greenland region with anomalous low pressure and high pressure, respectively. These were associated with a barotropic +west/−east or –west/+east dipole pattern, respectively, over Eurasia during the subsequent winter and spring seasons. Furthermore, these patterns led to positive and negative snow depth anomalies, respectively, over western Eurasia and the opposite snow tendency over eastern Eurasia during the subsequent spring. This variability in Eurasian snow patterns may play a crucial role in ISM and KSM. The co‐occurrence of ENSO variability also generates high‐ and low‐pressure anomaly patterns over the Indian Ocean that may be related to unfavourable or favourable ISM, respectively, while influencing the negative or positive phases of a Pacific Japan (PJ)‐like teleconnection pattern that may be related to unfavourable or favourable KSM, respectively. Therefore, coexisting ENSO forcing may play a dominant role in ISM and KSM, but Greenland sea ice forcing and Eurasian snow variation intensify the out‐of‐phase relationship between ISM and KSM.